This invention relates generally to a stage system for precisely positioning an article carried thereon. In another aspect, the invention is concerned with an exposure apparatus having such a stage system for positioning a wafer on a reticle, and also with a device manufacturing method using such an exposure apparatus.
FIG. 14 shows an example of a conventional stage system. A guide 52 is fixed on a base, not shown. A stage 51 which is slidably movable along a driving direction is supported by the guide. A workpiece 60 is placed on the stage. There are linear motors disposed on the opposite sides of the stage 51, for moving the stage in the driving direction. Linear motor stators 53 each comprise six flat coils 56 fixed to a stator frame 57, and they are fixed to the base, not shown, through fixing members, not shown.
A movable element 54 of the linear motor comprises an integral structure of four-pole magnets 58, being magnetized in the vertical direction, and yoke plates 55 which are disposed above and below the stator unit and fixed to the stage 51 without contact to the stator element 53. The six coils 56 are disposed along the driving direction at a pitch 1.5 times the pitch of the magnetic poles. The coil pitch corresponds to a 0.75 period of the basic wave of the magnetic density and, in terms of electric angle, to 270 deg. or xe2x88x9290 deg.
While the relative position of the coils 56 and the magnets 58 is detected by means of a sensor, not shown, coils 56 at positions spaced by 270 deg. or xe2x88x9290 deg. are selected sequentially and electric currents are supplied to them in an appropriate direction, whereby the magnets are driven In the same direction. Although the coil means has six phases in the sense that the coils 56 are interchanged sequentially, the motor comprises a two-phase motor.
In the stage system of the structure described above, an integral structure of yokes and magnets is moved. Therefore, the weight of movable components is large and stage acceleration is slow. Also, there occurs thrust ripple due to the coil interchanging during the driving. This is an external disturbance, disturbing high-precision positioning control.
FIG. 15 shows another example of a conventional stage system. A guide 52 is fixed on a base, not show. A stage 51 which is slidably movable along a driving direction is supported by the guide 52. A workpiece, not show, is placed on the stage, There are movable magnets 58 disposed on the opposite sides of the stage 51, and they are held by holding frames 59. Stators 53 to be associated with these movable magnets 58 each comprise single-phase colis 56 extending throughout the whole stroke of the stage 51. Each coil 56 is wounded coaxially around an upper yoke 55a or a lower yoke 55b, extending through the whole stroke.
In order to prevent eddy current resistance to be produced during relative motion of the magnets 58 and yokes 55, each yoke 55 comprises laminated steel plates as shown in the drawing.
In the structure described above, in response to supply of electric current to the single-phase coil 56, forces in the same direction and corresponding to the electric current are produced at every location within the stroke. Thus, only application of electric current in a desired direction is necessary. No coil interchanging is necessary throughout the stroke.
Since, however, in the stage system described above, high-speed relative motion between the magnets and yokes causes an eddy current in the yokes which applies a resistive force to the relative motion of the magnets and yokes. If the eddy current resistance is large, a large driving force is necessary for the stage. The yoke may be provided by laminated steel plates to solve this problem. However, assembling such long steel plages is not easy, and also supporting the yoke after assemblage is not easy. It is, therefore, practically difficult to produce a yoke of a complicated shape by use of laminated steel plates. Consequently, the yoke has a large weight.
Further, there is an attraction force caused between the yoke and magnet. If the stoke, that is, the length of the yoke, is large, flexure of the yoke as the magnet comes to the central portion of the stroke becomes large. Also, the flexure changes largely between the moment where the magnet is at the central portion and the moment where it is at an end portion. This excites vibration of the yoke. For these reasons, the yoke should be formed with a sectional area larger than that as required only for passage of the magnetic flux, to thereby reduce the absolute value of flexure. This means a large increase in dimension of the required sectional area. The increase in size of the yoke necessarily leads to an increase of mass of the yoke and, in contrast to reduction in weight of movable components, the stator becomes very heavy. Finally, when an X-Y stage mechanism is provided by a simple two-level structure, the movable stage must include a portion, having such a very heavy yoke, and a large acceleration is difficult to accomplish to such portion. Further, what is contributable to production of thrust is only the portion of the coil structure which is opposed to the magnet, and most of the apparatus is unnecessary with respect to the thrust production. Also, there is no large or unnecessary heat generation.
It is an object of the present invention to provide an improved high-speed and high-precision stage system, by which at least one of the problems described above can be solved.
In accordance with an aspect of the present invention, there is provided a stage system, comprising: a movable stage; a first driving mechanism having a magnet and a coil, for moving said stage along a predetermined direction; and a second driving mechanism for moving said first driving mechanism along the predetermined direction; wherein one of said magnet and said coil of said first driving mechanism is connected to the stage side, while the other is connected, together with a yoke, to the second driving mechanism side: and wherein, while a position or a speed of said stage is controlled as said stage is driven through said first driving mechanism, one of said magnet and said coil of said first driving mechanism connected to said second driving mechanism is moved substantially in synchronism with said stage.
In one preferred form of this aspect of the present invention, said magnet is provided at the stage side while said coil is provided at the second driving mechanism side. Said second driving mechanism may include a feed screw. Said second driving mechanism may include a linear motor. Said magnet and said coil may have substantially the same size with respect to the movement direction. Said yoke may comprise a ferromagnetic material of flat plate shape. Said coil may be wound around said yoke. Said coil may comprise a flat coil. Said first driving mechanism may include a plurality of coils. Said first driving mechanism may be operable to move the movable member two-dimensionally. Said coil may comprise a first coil for producing a driving force in a first direction with respect to said magnet, and a second coil for producing a driving force in a second direction with respect to said magnet. Said second driving mechanism may be operable to move, two-dimensionally, one of said magnet and said coil of said first driving mechanism as connected to said second driving mechanism. Said yoke may have a recess formed in a peripheral portion thereof.
In accordance with another aspect of the present invention, there is provided an exposure apparatus, comprising: a stage being movable while holding one of a wafer and a reticle thereon; a first driving mechanism having a magnet and a coil, for moving said stage along a predetermined direction; and a second driving mechanism for moving said first driving mechanism along the predetermined direction; wherein one of said magnet and said coil of said first driving mechanism is connected to the stage side, while the other is connected, together with a yoke, to the second driving mechanism side; and wherein, while a position or a speed of said stage is controlled as said stage is driven through said first driving mechanism, one of said magnet and said coil of said first driving mechanism connected to said second driving mechanism is moved substantially in synchronism with said stage.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.